The present invention relates generally to an analysis system for use with an electrical utility power system, and more particularly to an arc burst pattern analysis fault detection system for detecting high impedance, low current arcing faults on the power system. Arcing faults may be caused by, for example, downed, broken, tangled or dangling power lines, trees contacting the power lines, and various overcurrent fault situations.
Arcing faults are more difficult to detect than permanent overcurrent faults, which for instance, occur when a transformer fails. Most conventional overcurrent protection devices, such as fuses, reclosures, relays and the like, have time delays which prevent a temporary fault from de-energizing the power line. Only if the overcurrent fault persists does such a protection device de-energize the power line. Some arcing faults may initialize the timing circuits of the overcurrent protection devices but, by the end of the time delay, the high impedance nature of the fault limits the fault current to a low value. Such overcurrent protection devices cannot distinguish this low fault current from the levels of current ordinarily drawn by customers; hence, the line may remain energized even though a dangerous arcing fault exists on the power line.
Other methods of fault analysis have focused on determining the location of a fault, rather than a method and apparatus for detecting the existence of an arcing fault, as claimed below. For example, one earlier method for determining the location of a fault on a power circuit is proposed by Saha in U.S. Pat. No. 4,559,491. Saha determines the fault location and the type of fault on a transmission line, but does not perform fault detection per se. Saha computes the fault location using vector measurements to obtain the line impedance from which the fault location is determined. Moreover, Saha uses only the single fundamental waveform, ignoring the wealth of information contained in the remainder of the waveform.
Saha's system lacks the ability to detect the presence of an arcing fault. Unfortunately, the Saha method requires a steady state fault for effective determination of the fault's location. Since arcing faults may exhibit a highly variable behavior from one cycle to the next, the Saha approach is clearly ineffective for identifying arcing faults. Moreover, the Saha approach is generally ineffective for use in radial distribution circuits with multiple conductive paths. Furthermore, the apparent impedance of an arcing fault may well be within the acceptable impedance ranges for loads normally connected to a line. Thus, the Saha approach is clearly unable to discriminate arcing faults from these normal loads.
U.S. Pat. No. 4,281,386 to Kondow proposes a fault detection system based upon an impedance measuring scheme. Kondow indicates the presence of a fault when the impedance falls within a certain zone defined by Kondow. Kondow's system lacks the ability to detect the presence of an arcing fault. Arcing faults may exhibit highly variable behavior from one cycle to the next, thus rendering the Kondow approach ineffective. Furthermore, the apparent impedance of an arcing fault may well be within the acceptable ranges of loads normally receiving power from the line. The Kondow approach would either be unable to detect many arcing faults or would falsely identify normal loads as arcing faults.
In U.S. Pat. No. 4,719,580, Nimmersjo detects and locates faults using a traveling wave analysis technique. Such a traveling wave analysis requires very fast sampling of signals to capture the wavefronts. The Nimmersjo approach is unable to effectively detect an arcing fault. Nimmersjo relies upon traveling wave signals which may occur for faults as well as for normal switching events on a line. Thus, the Nimmersjo approach simply cannot discriminate between faults and switching events. Furthermore, Nimmersjo cannot effectively determine a location of a fault in a distribution circuit having multiple conductive paths.
Thus, a need exists for an improved arc burst pattern analysis fault detection system for electrical power utilities which is directed toward overcoming, and not susceptible to, the above limitations and disadvantages.